1. Field of the Invention
The present invention relates to a film forming apparatus for forming a thin film on a substrate.
2. Description of the Related Art
A manufacturing process of a semiconductor integrated circuit includes various film forming processes for forming several thin films on a substrate, such as a semiconductor wafer (hereinafter, referred to as a wafer). A so-called batch-type film forming apparatus may be used during a film forming process. Such a film forming apparatus includes a wafer boat holding a plurality of wafers at intervals, a reaction chamber accommodating the wafer boat, a support unit supporting the reaction chamber, a raw material gas supply pipe extended along the wafer boat inside the reaction chamber and for supplying a raw material gas for forming a thin film on the wafers to the wafers, and a heater disposed outside the reaction chamber and for heating the wafers held by the wafer boat.
Also, in the film forming apparatus, a temperature measuring unit is provided along the wafer boat so as to measure a temperature of the wafers. In order to protect the temperature measuring unit from the raw material gas, the temperature measuring unit may be inserted into a protection pipe extended along the wafer boat (for example, Patent Reference 1).
In the film forming apparatus, when a thin film is formed on the wafers, for example, the wafers are loaded on the wafer boat, the wafer boat is accommodated in the reaction chamber, the wafers held by the wafer boat are heated by using the heater so that a temperature of the wafers reaches a predetermined film forming temperature, and then the raw material gas is supplied. Accordingly, the raw material gas is decomposed by heat of the wafers, and a thin film is formed on the wafers by a decomposition product.
Here, the decomposition product is not only deposited on the wafers, but also on the wafer boat, the reaction chamber, and the protection pipe. Thus, if an outer surface of the protection pipe contacts an inner surface of the reaction chamber, the outer surface of the protection pipe may be adhered to the inner surface of the reaction chamber due to the decomposition product. In this case, it is not easy to separate the protection pipe from the inner surface of the reaction chamber during maintenance of the film forming apparatus, and the protection pipe may be damaged if the protection pipe is separated by force. Accordingly, careful work is required, and thus a time required for maintenance may be increased.
Also, if the outer surface of the protection pipe is adhered to the inner surface of the reaction chamber, a stress may be applied to the protection pipe while decreasing the temperature of the wafers after film formation, thereby damaging the protection pipe.
3. Prior Art Reference
(Patent Reference 1) Japanese Laid-Open Patent Publication No. 2002-270593